Rocky Mountains 1

Central United States

• What defines the prairie complex in the central U.S.?

  • treeless; less than 10% forested

  • Why?

    • Too dry; less than 15 inches of rain

    • Rain shadow effect (rain drops in coastal areas because clouds don’t make it over mountains)

Rain shadow effect

• Rain shadow: area of low rainfall on the leeward side of a mountain range, away from the prevailing weather system

  • as the clouds rise to move over the Rockies, their precipitation drops out as the air cools and condenses

  • Prairie: 15-20 inches of annual rainfall

  • Desert: less than 10 inches of rain

  • 

Rocky Mountains: Fast facts

• The Rocky Mountain Complex stretches from Alberta to Mexico

• States include MT, ID, ND, SD, KS, CO, UT, NM, NB, and part of TX, AZ, and WY

• Mountains are taller younger drier and more rugged than the Appalachians

• Formed 80-55 million years ago

• In Mexico, they become the Sierra Madre

Sierra Madre Mountains

• The Rocky Mountains split and become the Sierra Madre Mountains to the south, in Mexico

• Sierra: rocky, ragged mountain range

• Madre: mother

  • oriental: eastern, occidental: western

Rocky Mountains: Environmental gradients

• about 30% forest cover; forest is patchy

• Highest peak is Mt. Elbert, CO

• But the “base” is also high—about 5000 ft

• Lower average precipitation than the East

  • Denver: 12” annually

  • Salt Lake City: 14” annually

What are the key environmental factors that affect forests in the Rocky Mountains?

• Elevation

• Rainfall

• Aspect

• Topography

• Fire history

Lower elevations: water

Higher elevations: other factors

Rocky Mountain Region Principles forest types (lowest to highest elevation)

Rocky Mountain Forest Region Transition Zone

• Transition zone is between areas that are too dry and just wet enough for shrubs and small trees

• 4000-5500 ft elevation

• Less than 15” of rainfall

• Shrubby hardwoods (spacing and density)

• overgrazing

• sometimes called “sage-brush”

• Principle species

  • cambel oak

  • mountain mahogany

  • sagebrush

Rocky Mountain Forest Region Woodland Zone

• Found between 5500-6000 ft in elevation

• Short, widely spaced trees > competition for water

• Annual rainfall: 15-18 inches

• Commonly called Pinyon pine—Juniper Woodland

• Pinyon pine: pine nuts are an important and traditional food of the Navajo

• Principal species:

  • Pinyon pine

  • Rocky Mountain juniper

Rocky Mountain Forest Region Submontane Zone

• Found between 6000-7000 ft in elevation

• Annual rainfall: >18 inches

• Originally a fire-maintained savanna with widely spaced trees; today’s forests are denser

• Denfse stands prone to insects, disease, and wildlife

• Commonly called Ponderosa Pine Forest

• Principle species:

  • ponderosa pine

    • vanilla-scented, very thick bark that sloughs off during fire

    • open crowns dissipate heat

    • one of the most fire-resilient pines owing to the thick bark

    • fire resistance increases with age

    • 3 needles per fascicle; large cones

Rocky Mountain Forests

• Threats

  • Climate change causing changes in precipitation patterns

  • Recent history of fire suppression has caused fuel build-up and dense stands

  • Susceptible to beetle outbreaks and uncontrollable wildfires

Rocky Mountains 2

Rocky Mountain Geography

• Rocky Mountains

• Cascades

• Sierra Nevada

• Columbia Basin

• Great Basin

• Inland Empire

What are the key env. factors that affect forests in the Rockies?

• Rainfall

• elevation

• aspect

• topography

• fire history

• lower elvations—weather

• higher elevations—other factors

Rocky Mountain Forest Region—Montane Zone

• the Montane Zone varies more with latitude/geopgrahy than lower elevation forests

• Also the most biologically diverse

• WHY?

• Found between 7000-9000 ft in elevation

• Annual rainfall: >18 inches

• Species composition more variable depending on geography. We’ll see several examples.

• Forest structure ranges from open to closed canopy

• Some of these forests are fire adapted

• Principal species:

  • Douglas-fir

  • 2 varieties recognized: var. glauca and Pacific NW

  • Forms closed stands in some places, also grows in mixed stands

• Drier sites (south and west):

  • Douglas-fir

  • Quaking aspen

  • Ponderosa pine

• Moister sites (north)

  • Douglas fir

  • Western hemlock

  • Western redcedar

  • Grand fir

• Fire-driven sites

  • Lodgepole pine

    • rockies: serotinous cones

  • Western white pine

  • Western larch

  • Quaking aspen

  • Fire interval 100-300 years

  • Stand-replacing catastrophic fire

• Summary

  • Douglas-fir is the most widespread species; lots of variation by geography

  • Drier sites (south and west) get quaking aspen

  • Moister sites (north) and geography get western hemlock and western redcedar

  • Fire-adapted sites have lodgepole pine, which is adapted to periodic, stand-replacing fire

Rocky Mountain Forest Region Sub-Alpine Zone

• Spruce-fir forest: 9000-11000 ft > 18” rainfall

  • highest forest zone below treeline

  • rainfall much less than the East

  • thin, rocky soils

  • high winds, cool, short summers, cold winters

  • disturbance includes avalanches

• Evergreen canopy

• Little to no understory—too rocky

• Stunted near treeline

• Principle species:

  • Englemann spruce, subalpine fir

Rocky Mountain Region Alpine Zone

• >11,500 feet—climatic treeline

  • very harsh climate

  • extremely thin, rocky soils

  • high winds, cool, short summers, cold winters, deep snowpack

  • Alpine plants in miniature

  • Not quite tundra (no permafrost)

  • Protected areas can host a few adaptable pine species

  • Sprawling form

  • Bristlecone pine, limber pine, whitebark pine